6 INTRODUCTION. 



tinal canal of insects and worms, can scarcely be devoid of organic 

 components. In general it cannot be contested that the vegetable 

 kingdom prepares from inorganic nature those substances which 

 serve for nutriment to the animal kingdom. Albumen and Fibrin, 

 the principal constituents of the blood of animals, are already 

 present in the parts of plants which they consume. But still, on the 

 other hand, there are plants which grow on other plants, and thus 

 apply to their own development the matters which have been pre- 

 pared by those organic bodies. 



Scruples arising from such considerations must not mislead us 

 to consider plants and animals as belonging to one and the same 

 kingdom. Perhaps the following remarks may help to distinguish 

 them from each other. 



If we consider the nutrition, we perceive that animals convey 

 their food by one or more apertures into a common cavity, the 

 stomach or intestinal canal, from which the prepared matters are 

 absorbed and applied to the nutrition of the whole body. Thus the 

 intestinal canal is for animals what the soil and air are for plants. 

 The plant is consequently so constructed that its surface has the 

 greatest possible extension : in the animal all is contrived for union 

 round a center. Moreover the plant, which receives nutriment by 

 means of its surface and the parts there situated, (pores, hairs, &c.) 

 has no need to seek for food : it lives in the midst of its food : when 

 this is deficient it cannot move and must consequently die. The 

 animal, on the contrary, is destined to seek its food, which it must 

 conduct into its intestinal canal : it moves therefore when nutriment 

 is deficient. Let it not be here objected that plants move towards 

 the light, and send larger roots towards the side where moisture is 

 more abundant for this would be to confound growth with motion. 

 The stimulants (light, moisture, &c.) act upon the plant, and there- 

 fore its growth is more vigorous in that direction. The animal has 

 independent motion which is excited by internal stimuli. Hence 

 sensation is ascribed to animals. In the higher animals it is known 

 that the contraction of the muscles is under the influence of the 

 nervous system : that the stimuli, of whatever kind, if they pro- 

 duce motion, act upon the nerves and through these upon the 

 muscles. Comparative Anatomy, it is true, has, in some animals, 

 hitherto failed to demonstrate a nervous system; but it does not 

 therefore follow that these animals do not possess sensation, any 



